The invention relates to a vehicle steering system having a manual steering device, particularly a driver operated manual steering wheel, as well as a motor-driven actuating unit which is assigned to the steered vehicle wheels. The manual steering device is operatively connected by way of a control system whose control device is, on the one hand, for the purpose of obtaining a desired-value actual-value comparison, connected on the input side to a desired value generator operated by the manual steering device and to an actual value generator recording the steering angle of the steered vehicle wheels. On the other hand, the manual steering device is operatively connected on its input side with sensors for detecting forces in the vehicle steering system.
Currently, passenger cars and similar motor vehicles are, as a rule, equipped with hydraulic power steering systems. In this case, the manual steering wheel is mechanically coupled in a forced manner with the steered vehicle wheels. The steered vehicle wheels are also connected to the drive with a motor-driven actuating unit, which is controlled as a function of forces or torques transmitted between the manual steering wheel and the steered vehicle wheels. For this purpose, parts, i.e., shaft parts, of the mechanical driving connection between the manual steering wheel and the steered vehicle wheels are resiliently connected with one another so that the parts or shaft parts carry out, corresponding to the respective active forces or torques, a substantial actuating stroke or a substantial rotation relative to one another. By means of this actuating stroke or this relative rotation, a servo valve is then operated which controls the hydraulic actuating unit.
Optionally, an electric actuating unit may be controlled by this actuating stroke or the relative rotation.
In the case of airplanes, it is known to connect tail units and wing flaps and the like with assigned manual devices only with respect to the operation by way of a control system. The manual device actuates a desired value generator and the wing flaps and the tail units actuate an actual value generator. The control device of the control system subsequently processes the signals of the desired value and actual value generator to effect a desired-value actual-value comparison and, as a function of the result of this comparison, controls motor-driven actuating units for the tail units and the wing flaps. This concept, which is also called "fly by wire", has become so reliable that even passenger planes have corresponding equipment.
In principle, it is also possible to provide comparable arrangements in the case of vehicle steering systems, as indicated in German Patent Document DE 42 321 256 A1, which shows a vehicle steering system of the initially mentioned type. According to the DE 42 32 256 A1, the control device is also capable of carrying out an autonomous steering intervention, for example, in order to counteract disturbances caused by cross wind.
Another steering system of the initially mentioned type is indicated in German Patent Document DE 42 07 719 A1.
In the case of steering systems of this type, the control device can also control a manual force actuating device so that to the driver feels a steering resistance at the manual steering device which changes according to the driving conditions. According to German Patent Document DE 42 32 256 A1, the manual force actuating device can be constructed as an electric motor or as a hydraulic unit. In connection with such a hydraulic unit, German Patent Document DE-42 07 719 indicates that the control device for controlling the hydraulic unit can operate a control valve.
European Patent Document EP 0 539 823 A1 shows a steering system of the initially mentioned type where a mechanical drive-through between the manual steering device and the steered vehicle wheels is not completely eliminated. However, it is only provided to switch the mechanical drive-through inoperative when the control system operates without errors in order to implement in the normal operation parameter-dependent steering kinematics which deviate from the mechanical drive-through. In contrast, in the case of disturbances in the control system, the mechanical drive-through is to become active.
From the printed document "Letters on Measuring Techniques 31 (1995)", Volume 1, Pages 13 to 18, wheel hubs with power sensors are known for measuring the strains on vehicles during operation and thus assist the design of chassis systems as well as proving stability when developing new vehicles.
From the journal Automobil-Industrie (1991), Volume 4/5, Pages 303 to 309, an electronic characteristic-diagram steering am system for utility vehicles is known. In this case, power assistance is changed as a function of parameters. Specifically, power assistance is changed as a function of forces and torques at vehicle wheels.
From the two latter documents, it is also known to monitor various force components separately.
German Patent Document DE 44 22 386 C1 relates to a power steering system with a reaction power controlled as a function of parameters, where this control can take place as a function of the signals of pressure sensors enabling the detection of forces which occur at the hydraulic servo motor.
The journal Kraftfahrzeugtechnik (1994), No. 11, Pages 36 to 38, shows active chassis systems, where the stability of the vehicle during steering maneuvers can also be increased by the automatic operation of the brakes of individual vehicle wheels as well as by the actuation of controllable spring or support assemblies.
It is an object of the invention to provide an advantageous arrangement for a steering system of the initially mentioned type.
According to the invention, this is achieved by connecting the control device to the input side with force or tension sensors on at least one wheel carrier of the steered vehicle wheels.
The invention is based on the general idea of sensing forces acting upon the steered vehicle wheels as directly as possible so that the control device can record the introduction of disturbance variables from the road by way of the steered vehicle wheels without any time delay, and examine its plausibility by means of other input quantities. This permits a multi-redundant system, where the redundant signals or the redundant information determined from the signals originate from differently structured and arranged sensors. There is also the advantageous possibility that, as a function of forces active on the steered vehicles wheels, the control device controls or influences a manual force actuator without delay. This has the purpose of simulating or modulating, as a function of the respective driving conditions, an actuating force on the manual steering device or on the manual steering wheel which can be felt by the driver.
On the whole, because of the invention, extraordinarily high control dynamics can be achieved because all forces acting upon the steered vehicle wheels can be "noticed" by the wheel-carrier-side sensors at the earliest possible point in time before, for example, a larger pressure change has occurred in a hydraulic actuating unit or a larger change of force has occurred in the case of an electric actuating unit, or the gearing elements between the steered vehicle wheels and the actuating unit have carried out recordable strokes or rotations.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with he accompanying drawings.